U.S. Pat. No. 5,796,214, issued to the present inventor and assigned to the instant assignee, discloses various gas discharge lamp ballast circuits of the type using gate drive circuitry to regeneratively control a pair of serially connected, complementary conduction-type switches of a d.c.-to-a.c. converter. The gate drive circuitry includes a feedback circuit which obtains a signal representing load current by including a feedback inductor mutually coupled to an inductor in the load circuit. The mutual coupling is typically carried out by forming the feedback inductor as a tap of the load inductor. This requires the load inductor to be custom designed, increasing its cost. If such a tapped inductor could be eliminated, the cost of the ballast could be reduced significantly.